Extracapsular surgical procedure and surgical referencing instrument therefor

ABSTRACT

A method and device for finding isometric points in the joints of mammals for use in surgical repair of a joint. Isometric points are first identified in radiographic or other two dimensional images and then located in the actual joint. A method for repairing a cruciate ligament-deficient canine stifle employing the method and device for finding isometric points is described. A method and apparatus for locating the axis of rotation of a joint is also described.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a continuation-in-part of copending application Ser. No.10/934,269 filed on Sep. 3, 2004, entitled Extracapsular SurgicalProcedure for Repair of Anterior Cruciate Ligament Rupture and SurgicalReferencing Instrument Therefor; which claims the benefit of U.S.Provisional Patent Application No. 60/499,859 filed on Sep. 3, 2003.

BACKGROUND OF THE INVENTION

This application relates to surgery for repair of injured articulatingjoints between bones in mammals, and to a method and a device for usetherein.

The caudal and cranial cruciate ligaments are the primary stabilizers ofthe stifle joint in mammals such as canines. The caudal cruciateligament originates from the lateral side of the medial femoral condyleand inserts on the medial aspect of the popliteal notch of the tibia.The cranial cruciate ligament originates from the medial side of thelateral femoral condyle and inserts on the cranial medial tibialplateau. In canines, the stifle joint is normally capable of flexion andextension with a 110 degree range of motion, varus and valgusangulation, and internal and external rotation. The stifle is extendedby the quadriceps muscle group. Injury to a cruciate ligament willcommonly result in destabilization of the joint. The joint must besurgically stabilized following such an injury.

Current surgical techniques for anterior cruciate ligament replacementand/or stabilization in canine knee or stifle joints are grouped intoextracapsular procedures and intracapsular procedures. Intracapsularprocedures require a graft from an adjacent tissue such as the straightpatellar tendon or the fascia lata, which is detached from its originand inserted or repositioned through tunnels bored in the distal femurand/or proximal tibia. This surgery is done inside the joint capsule,with both ends of the transplant being fixed to the walls of the tunnelsand/or adjacent bone. Extracapsular procedures use tissues or sutureimplants placed outside of the joint capsule in order to stabilize thejoint.

Determination of the isometric relationship between location of theorigin and location of the insertion of a ligament repair structureforms the foundations of intracapsular surgical repair of ligaments inhumans. These same isometric relationships may be determined and usedfor extracapsular repair of cruciate or other ligament failure in thejoints of any mammal. However, current extracapsular surgical procedureshave not addressed the optimal placement of transplant tissue or sutureat the isometric points.

What is needed then is a surgical device and procedure for repair of aligament that provides for the determination of optimal points for theattachment of graft, transplant, or other tissues or tension-bearingmaterials in an extracapsular procedure.

SUMMARY OF THE INVENTION

As a first aspect of a method according to the disclosure herein, adevice and method for determining spatial relationships in a joint of amammal comprises obtaining two-dimensional images of the joint in flexedand extended positions, finding a reference point on one bone of thejoint and at least approximately locating an isometric point on anotherbone in the joint by using the two dimensional images, and thereafterusing a measuring and positioning device to locate those points in themammal joint.

According to another aspect of the disclosure herein a locating andpositioning device is provided by means of which a reference point canbe marked on a first bone of a joint and an isometric point can belocated and verified. As another aspect of the method disclosed thelocating and positioning device can be used to aid in establishing ahole in at least the second bone to receive a tissue anchor as part of agraft-forming procedure.

In accordance with an aspect of the device, the locating and positioningdevice can be adjusted and fastened to measure spacing between a pair oflocating portions.

As a feature of one embodiment of the device the locating portions arecarried as the distal ends of respective area of a pair of armsadjustably pivotable with respect to each other, and at least one of thelocating portions is adjustable with respect to the arm on which it iscarried.

In accordance with one aspect of a method of using the locating andpositing device one locating portion can be fastened to one of a pair ofbones that meet in an articulating joint, and the other locating portioncan be moved relative to the first to find and verify the location of anaxis of rotation of a joint that can move in a hinge-like fashion, inorder to determine where to place an external fixation device for use insupporting such a joint during the process of healing after an injury tothe joint.

The foregoing and other objectives, features, and advantages of theinvention will be more readily understood upon consideration of thefollowing detailed description, taken in conjunction with theaccompanying drawings.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 is a view of a radiograph of a canine stifle joint in a fullyflexed position, showing use of a pair of dividers to measure a distancebetween respective points on the tibia and femur shown in theradiograph.

FIG. 2 is a view of a radiograph of the same stifle joint shown in theradiograph depicted in FIG. 1, with the stifle joint in its fullyextended position, showing use of a divider to measure between aselected point on the tibia and a point on the femur shown in theradiograph.

FIG. 3 is an isometric view of a measuring and positioning device whichis an exemplary embodiment of one aspect of the present invention.

FIG. 4 is a top plan view of the device shown in FIG. 3.

FIG. 5 is a bottom plan view of the device shown in FIG. 3.

FIG. 6 is an isometric view of a measuring and positioning device whichis another exemplary embodiment of an aspect of the disclosure herein.

FIG. 7 is a side elevational view of the device shown in FIG. 6.

FIG. 8 is a top plan view of the device shown in FIG. 6.

FIG. 9 is an elevational view taken from the outer end of the deviceshown in FIGS. 6, 7, and 8.

FIG. 10 is an isometric view of a measuring and positioning device whichis another embodiment of an aspect of the present invention.

FIG. 11 is a simplified frontal view of a partially dissected stiflejoint of a left leg of a canine, with the skin and other superficialtissue removed for the sake of clarity together with the device shown inFIGS. 3, 4, and 5 in use in connection with surgical repair of thestifle joint.

FIG. 12 is a simplified lateral view of the stifle joint of the legshown in FIG. 11, with the skin and other superficial tissue removed forthe sake of clarity, and showing the device shown in FIGS. 3, 4, and 5in use with the stifle in a fully flexed position.

FIG. 13 is a simplified lateral view of the stifle joint of the left legof a canine, with the skin and other superficial tissue removed for thesake of clarity, and showing the device shown in FIGS. 3, 4, and 5 inuse with the stifle in a fully extended position.

FIG. 14 is a lateral view of the stifle joint of the left leg of acanine, with skin and other superficial tissues removed for clarity, andshowing use of the device shown in FIGS. 3, 4, and 5 in connection withforming an autograft to repair an injury in the joint.

FIG. 15 is a view of a portion of a stifle joint, showing a tissueanchor in place in the femur and sutures connected with the anchor beingused to attach a portion of the fascia lata to the tissue anchor.

FIG. 16 is a view of the same area of the canine stifle that is shown inFIG. 15, at a subsequent step of the preparation of an autograft as partof a repair procedure.

FIG. 17 is a rear elevational view of a canine hock, showing use of thedevice shown in FIGS. 3, 4, and 5 to identify the location of an axis ofrotation of the hock joint.

FIG. 18 is a view of the hock joint and the device shown in FIG. 17,with the device being used to identify the location of the axis ofrotation of the hock.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

In a typical articulated joint, the ends of the bones which meet in thejoint operate as cams such that when the joint is flexed and extendedthe distance between a given first point in a first bone and a secondpoint on the second bone changes depending on the degree of flexion andextension. However, points typically exist in joints that have what canbe described as an isometric relationship. The distance between a givenpoint on one bone and its isometric point on the second bone changesduring flexion and extension but is the same at full flexion and fullextension. Such points can be said to have an isometric relationship,and herein will be referred to as isometric points. When connectivestructures such as cruciate ligaments in a joint are damaged and graftsor other replacement or substitute structures are employed to repair thejoint, these replacement structures should ideally be fastened to pointswhich have such an isometric relationship, in order to facilitate theproper function of the joint. When the replacement structure is attachedat such isometric points, it is under equal tension at each limit ofnormal range of motion of the joint after surgical repair.

Referring to the drawings, which form a part of the disclosure herein, ameasuring and locating device and a method for its use as disclosedherein permit a surgeon to locate appropriate isometric points inarticulated mammal joints, optimally after those points have beenpreviously approximated or identified in radiographic or othertwo-dimensional images of the joint. A method of repairing a torncranial cruciate ligament, a relatively frequent and significantlydebilitating injury occurring in the stifle or knee joint in canines,and use of such a measuring and locating device to repair a cranialcruciate ligament in a dog's stifle joint is explained herein. Thedevice and method may also be used to locate isometric points in anymammalian joint. The device and method may also be used to locate othermedically relevant points, such as in locating an axis of rotation of ahinged or ginglymus type joint of any mammal.

In placement of a replacement structure such as a graft, suture, orother structure in a joint, a first point of attachment of a replacementstructure must be determined. In the exemplary surgical proceduredescribed below, the joint to be repaired is a stifle, or knee, joint ofa canine, although the procedure is generally the same in the stifle orknee of other mammals, and the device can be used to find medicallyrelevant points in many other mammalian joints. As shown herein, thereplacement structure to compensate for a torn anterior cranial cruciateligament is an autograft 12 composed of a portion of the fascia lata andthe cranial insertion of the biceps femoris muscle. These structuresinsert naturally at Gerdy's Tubercle 20. The combined insertions of thefascia lata and cranial insertion of the biceps femoris muscle onGerdy's Tubercle form a strong, dynamic, vascularized ligamentousinsertion at this tubercle. Because these structures are alreadyattached to the tibia at Gerdy's Tubercle, and because Gerdy's Tuberclehas an isometric relationship with a point on the lateral femoralcondyle, Gerdy's Tubercle is a logical first point of attachment for thereplacement structure employed in this particular surgery. The preferredpoints of attachments to be used may vary in other situations, dependingon the joint, the surgical technique used, the nature of the replacementstructure employed, and other factors.

An isometric point on the lateral femoral condyle 18 is a logical choicefor the second point of attachment when Gerdy's Tubercle is used as afirst point of attachment. In the frontal plane and sagittal planes, theline defined by the origin and insertion of the CCL lies approximatelyparallel to a line drawn from Gerdy's Tubercle to the isometric point onthe lateral femoral condyle. The dorsal view of the stifle joint showsthat the origin and insertion of the cranial cruciate ligament roughlyparallels the line drawn between Gerdy's Tubercle and the determinedisometric point on the femoral condyle. Therefore, an autograft attachedat these points can function well to stabilize the stifle.

The first step repairing such an injured stifle is to prepare full scaleor known scale latero-medial radiographic or other two-dimensionalimages of the joint to be stabilized. See FIGS. 1 and 2. It ispreferable to take radiographic images of both corresponding joints forcomparison. For example, where a dog's stifle is to be repaired, imagesshould be taken of both the dog's stifles. Images are taken with thejoint in at least two positions in its range of motion, preferably infull extension as shown in radiograph 19, FIG. 2, and in full flexion asshown in radiograph 17, FIG. 1.

The point which is isometric relative to Gerdy's Tubercle is identifiedon the two dimensional images by determining the point on the femoralcondyle which is equidistant from Gerdy's Tubercle when the joint is infull flexion and when the joint is in full extension, as shown in FIGS.1 and 2. This point can be identified on the 2-dimensional images 17 and19 using an ordinary compass or pair of dividers 24, ruler, or any otherdevice suitable for measuring spatial relationships in two dimensions.The isometric point usually lies in a region near the physeal line ofthe caudal femoral condyle at the caudal aspect of the condyle. Thisregion forms the isometric region in which the isometric point may befound. If a compass or divider 24 is used, the first compass or dividerpoint is placed on Gerdy's Tubercle 20. A first “trial” point 21 islocated antero-ventral to the lateral femoral fabella on the lateralfemoral condyle 18, and the second point of the compass is adjusted tothat distance. A first determination of the isometric region is testedon the flexed view, by maintaining the first measurement and placing thefirst compass 24 or divider point on Gerdy's Tubercle 20 as shown in thesecond image. The compass or divider is used to measure a separationdistance 22 between Gerdy's Tubercle 20 and the trial point 21. Byrepeating this reiterative process back and forth between the images ofthe joint in extended and flexed positions, the isometric point ispreliminarily determined. If the separation distance 22 is the same inhe flexed view and the extended view, the isometric point has beenpreliminarily determined. Once located, the imaged isometric point ismarked on the radiographs and the distance between Gerdy's Tubercle andthe imaged isometric point is measured with a specialized measuring andpositioning device 10 such as that shown in FIGS. 3-5.

The device 10 is capable of fixing a location on each of two bones. Thedevice possesses two distal ends 28 equipped with locating portions 30,each of which is associated with a marking element 32. The locatingportions 30 may optionally be selectively fixable with respect to eachother so that they cannot move with respect to each other. The devicemay also include a scale 34 capable of measuring or providing a directindication of the distance between the two marking apparatus.

As shown in FIGS. 3-5, the device 10 possesses a main body 52 which caninclude a pair of arms 36 which are interconnected and extend from atleast one pivot joint 40. The pivot joint 40 may include one or morerivets, pins, or other connectors. The arms 36 are connected closely toeach other or to a common member by the pivot joint 40 or joints, sothat they can move smoothly and precisely relative to one another. Atthe distal end 28 of each arm 36 is a respective locating portion 30.The locating portion 30 may include a cannulated receptacle forreceiving and holding a marking element 32 such as a Steinman pin, aKirschner wire or K-wire, or other pin, wire, tack, or any otherstructure capable of being affixed to bone. These marking elements 32should be affixable to bone without a pre-drilled hole. The markingelement 32 is preferably removable from the locating portion 30, but thelocating portion 30 may hold the marking element 32 firmly and minimizemovement of the marking apparatus. The locating portions 30 may hold thepins or wires approximately perpendicular to a plane defined by the armsof the device. At a point between the pivot joint 40 and the distal ends28 of the arms a connecting member 37 and locking mechanism 38 may belocated. In the device as shown, the connecting member 37 may bepermanently attached to one arm, and may consist of a flat membermounted to one arm and extending toward and in proximity to a lockingmechanism 38 which is mounted to the other arm. The locking mechanism 38may be a thumbscrew threaded in a slot in the connecting member 37attached to the second arm so that when tightened it fixes the distancebetween the arms. When the locking mechanism 38 is loosened, the armsmay move freely with respect to each other. When it is tightened, theyare held in a rigid or semi-rigid relationship with respect to oneanother. The locking mechanism 38 and connecting member 37 may serve tolimit the distance to which the arms may be spread.

The device may include a scale 34 which is marked such that distancebetween the locating portions or marking elements may be gauged, eitherby trigonometrically determining the distance between the distal ends ofthe arms, or by specifying the angle created by the two arms at thepivot point, or by other means.

The locating portions 30 of the device may be cannulated threadedcomponents 42 capable of receiving or holding a marking element 32 suchas a pin or a wire. These components may also include locking members 44located thereon such that their position with respect to the body orarms 36 is independently fixable, so that one locating portion 30 canthus be arranged so that it extends further below the arms 36 or body 52than the other in order to accommodate placement on a joint having jointsurfaces at different elevations with respect to each other. In FIG. 3,for example, the locating portions include externally threaded tubes 42which are held within threads defined in an enlarged portion of thedistal ends 28, and the elevation of each locating portion 30 can bechanged by screwing or unscrewing the component 42. The threadedcomponents 42 can also include rough-surfaced areas 50 that facilitategripping so that a surgeon can easily change the elevation or positionof the locating portion during surgery. The threaded cannulatedcomponents 42 may be oriented parallel with each other so that themarking elements 32 can be placed into their respective positionsparallel with a hinge axis of the joint being repaired.

A device 10, shown in FIGS. 6-9 is similar to the device 10, but issomewhat simpler in structure, lacking the threaded cannulated component42 and instead optionally having a cannulated portion 46 extending upfrom the distal end portions 28.

As shown in FIG. 10, a device 11 which is another alternative embodimentof the measuring and positioning devices 11 provides a linear member orbody 52 which may be square in profile or otherwise shaped so as to keeplocating portions 30″ aligned with each other. The linear member or body52 may have a handle portion 54 at one end which can be used for holdingand rotating the device. The body 52 carries a pair of locating portions30″ with which marking elements 32 are associated. The position of oneor more locating portions 30″ is adjustable and may be lockable withlocking devices 55. A scale may be associated with body 52.

To repair the stifle in which the cranial cruciate ligament has failed,once the patient is prepared for surgery, a skin incision is madeextending from lateral aspect of the patella to the lateral aspect ofthe insertion of the straight patellar tendon on the tibial tuberosity.Subcutaneous tissues are dissected, undermined, and retracted asnecessary. An incision 56 is made that extends from the lateralinsertion of the straight patellar tendon along the lateral border ofthe straight patellar tendon proximally to the base of the patella. Thejoint capsule is preserved. The insertion of the fascia lata and thecranial branch of the biceps femoris muscle is identified visually anddefined at Gerdy's Tubercle 20 by careful blunt dissection using asuitable instrument, such as a mosquito forceps. Another incision 57 maybe made along the caudal border of the graft 12. The forceps is forcedthrough the thin fascia at the caudal border of the biceps femorisinsertion at the caudal aspect of Gerdy's Tubercle. The tissue to beused as a graft 12 is thus defined. The strongest point of insertion 58of the graft 12 is identified at Gerdy's Tubercle 20. This point willserve as the first, or distal, proximal isometric point, indicated bythe reference numeral 58 in the drawings.

The measuring and positioning device 10 is aligned so that a firstlocating portion 62 and a marking element 32 held therein are parallelto the transverse axis of the tibial plateau and the arms of the deviceare parallel to the long axis of the shaft of the tibia on the frontalview, FIG. 11. The locating portions 30 and marking elements 32 shouldthus be parallel with each other and normal to the plane in which thetibia normally moves. The measuring and positioning device 10 is placedon the joint area so that with the measuring and positioning devicealigned as previously described, the first locating portion 62 contactsGerdy's Tubercle 20 when the second isometric point locating portion 64contacts the lateral condyle of the femur, as shown also in FIGS. 12 and13. A 1.5 mm (or 2 mm) K-wire 32 is then driven through the Gerdy'sTubercle locating portion 62 into Gerdy's Tubercle 20.

At this point, it may be necessary to extend the skin incision caudallyto gain additional exposure of the lateral femoral condyle. With softtissues retracted caudally to expose the isometric region on the lateralfemoral condyle, a second marking element 32 is inserted into the secondlocating portion 64. If a K-wire is used as the marking element 32, itshould be placed so that the blunt tip 70 of the wire is down,contacting the periosteum of the lateral femoral condyle 18, which canbe located initially by probing to locate the fabella 66 and the spacebetween the fabella and the condyle 18 of the femur, and then proceedinga small distance anteriorly, referring to the radiographs 17 and 19, tolocate the isometric region 61. With the device 10 set and fixed at theisometric distance previously determined by measurement of theradiographic images 17 and 19, the isometric region 61 is determined byflexing and extending the limb. The device 10 remains placed on top ofthe leg with the marking element 32, such as a K-wire held in the firstlocating portion 62 attached to the bone at Gerdy's Tubercle 20 and themarking element 32, such as another K-wire, held in the second locatingportion 64 and resting against the radiographically identified isometricpoint, as shown in FIGS. 12 and 13. The surgeon then uses the instrumentto determine whether the radiographically identified imaged isometricpoint is truly the actual isometric point 60. If it is, as the leg isflexed and extended the marking element 32 held in the second locatingportion 64 will rest on the same place at both full extension andflexion. That is, the separation distance 22 will be the same at bothfull extension and full flexion.

Once the surgeon has determined the actual isometric point, the K-wireis removed and replaced in the second locating portion 64 with thesharpened tip 68 down, contacting the periosteum at the previouslydetermined isometric point 60. The locking mechanism 38 is loosened, andthe sharp end of the K-wire 68 is advanced superficially into theperiosteum. Once the K-wire 60(a) is affixed to the bone at theisometric point, the locking mechanism 38 is loosened and the leg isagain flexed and extended, and the scale 34 is observed in order toconfirm that the marking member is affixed to the isometric point. Ifreading on the scale of the device is equal at both limits of range ofmotion the location of the isometric point is verified. The scalereading may decrease by about 10-15% through intermediate range ofmotion due to the cam configuration of the femoral condyles. Thisvariance illustrates the relief of tension on the cruciate ligamentsduring the swing phase of the normal gait.

When the isometric point is identified and verified, the K-wire or othermarking element 32 is driven deep into the isometric point 60 at the 18lateral femoral condyle. The device 10 and the K-wire or other markingelement 32 at Gerdy's Tubercle 58 are removed. This leaves the singleK-wire or other marking element 32 seated in the isometric point 60.

At this point it is possible to slide a cannulated conical periostealburr over the K-wire at the isometric point. With superficial softtissues retracted, the periosteum is roughened by gently rotating theburr around the K-wire with moderate pressure. The burr is withdrawn andany adherent periosteal tissue is retrieved and returned to theisometric graft site. Alternatively, the periosteum may be roughenedwith a sharp periosteal elevator.

A bone/tissue anchor 72 pre-threaded with two strands of suture material76, 78 (four ends thus available) is placed into the hole created at theisometric point 60 and driven into the femoral condyle 18. While theK-wire is still seated in the bone, a cannulated anchor (not shown) canbe slid down the K-wire. Otherwise, the K-wire or other marking element32 is removed, and the hole it leaves in the bone marks the placement ofthe anchor. A self-tapping threaded anchor that can be nearlycountersunk into the femur may be used. An appropriate suture materialmay be of braided ultra high molecular weight (UHMW) polyethylene, andmay be non-absorbable. An example of such a suture material is Telelex,Inc.'s “Force Fiber” product. At this point in the procedure, it isadvisable to perform an arthrotomy and examine intra-articularstructures for damage and repair if necessary. The arthrotomy is closedwith standard surgical technique.

The next step is to define the cranial proximal and distal limits of theautograft. The previous incision 56 at the lateral-most fibers of thestraight patellar tendon is continued proximally to the proximal limitsof the patella and the cranial border of the biceps femoris muscle.Blunt dissection separates the fascia lata from the underlying jointcapsule and preserves the patellar ligament and the origin of the longdigital extensor. This blunt dissection continues caudally to theisometric point 60 on the femur and frees the tissue to be used as agraft 12 from underlying soft tissue. The proximal, distal and caudallimits of the graft 12 are left undisturbed to ensure maximal bloodsupply and tissue strength. The fibers of the fascia lata and bicepsfemoris (ilio-tibial band) are traced from the anchor at the isometricpoint 60 on the femur to the insertion at Gerdy's Tubercle 20. Thedirection of these fibers determines the alignment of the graft, andfibers thus are properly aligned to form the “core” of its strength.

As shown in FIGS. 15 and 16, the graft 12 is attached to the anchor 72using the suture material 76, 78. The four suture ends are used forgraft traction, graft transfixing and graft bundling sutures. The firstpair of strands of anchor suture 76 are used as a “traction” suture. Thestifle is placed in extension. The first set of suture strands transfixthe graft 12, passing from the tissue anchor through the deep surface ofthe graft 12 and exiting approximately 10 mm distal to the anchor,approximately 5 mm apart, on the superficial surface of the graft 12. Asthe suture 76 is tightened, it will draw the graft 12 towards the anchor72, gradually increasing the tension on the graft. As the tension isincreased, drawer motion will be eliminated and the graft 12 will bedrawn down into the prepared periosteal graft site 60. At this point,the stifle is tested for range of motion, stability and isometriccorrectness. When these criteria are met, the first “traction” suture 76is tied. The second pair of suture strands 78 are then passed deep tothe graft, exiting distal to the anchor 72 approximately 10 mm apart.Tightening these strands will place more tension on the graft, and willbegin to “bundle” the graft. The second pair of traction sutures 78 aretied, but are not trimmed short, but rather, are left long for theirnext function, bundling, and re-enforcing the graft. The graft is“bundled” or “rolled” from a flat graft into a tube configuration with acontinuous “baseball stitched” suture pattern, as shown in FIGS. 15 and16, maintaining the previously noted alignment with the iliotibial band.Soft tissues are then closed in routine manner.

As healing occurs, the graft may undergo ligamentization, possibly duein part to the contact with the periosteum and cortical bone.

The foregoing illustration explains how the measuring device may be usedto determine isometric relationships useful in repairing the cruciateligament of a dog using an autograft formed of the fascia lata andbiceps femoris. However, the device 10 may be used to determineisometric relationships during repairs of the structural ligaments inany mammal joint.

Determination of biometric relationships may be useful for otherpurposes, such as determination of the axis or point of rotation of anyjoint that can operate in a hinge fashion, which aids in the correctreplacement of external fixation devices. As illustrated in FIGS. 17 and18, in a joint capable of moving in a hinge fashion, the center ofrotation can be thought of as the center of a circle 84, with a set ofreference points 82 having a type of isometric relationship with thecenter of rotation arrayed at the peripheral boundary of the circle 84around the center of rotation 80. Therefore, the center of rotation of ajoint may be determined with this measuring and positioning device 10.Determining the center of rotation is important when stabilizing afracture or orthopedic condition that requires the adjacent hinged jointremain functional. Malleolar shearing injuries, for example, arecommonly treated by stabilizing a hinge-type joint with a hingedexternal fixation device. Matching the center of rotation of the jointwith the center of rotation of the hinged fixation device provides theideal rotational relationship and maximum stability of the fracturefragments while, at the same time maintaining maximum range of motionfor the joint.

The measuring device 10 can be used to locate the center of rotation 80of a joint and guide placement of an external fixation device. First,one locating portion or marking element 88 is located at an arbitrarilychosen initial point 82 proximal or distal to the joint. This convenientlocation is outside the joint. Preferably, this initial reference point82 is also the location of a transfixation pin commonly used in externalfixation devices. Then, the second locating portion or marking element90 is located in the joint approximately at the center of rotation 80 ofthe joint. The axis or center of rotation 80 will be a lineperpendicular to the axis of the bone in which the reference point islocated. Accordingly, the instrument is placed normal to the planedefined by the axis of the bone, and perpendicular to the axis of thejoint. The joint is then moved through its range of motion. If thesecond member 90 is properly located at the center of rotation of thejoint, the marking elements 88 and 90 of the device will not move towardor apart from each other when the joint is moved. If the second markingelement 90 is not properly located, the movement of the joint will causethe device 10 to move, and the movement will be visible by observing thescale 34 on the device or the device itself. If the first placement ofthe instrument does not prove to be at the center of rotation, adifferent point is selected and tested until the center of rotation isidentified.

The terms and expressions which have been employed in the foregoingspecification are used therein as terms of description and not oflimitation, and there is no intention, in the use of such terms andexpressions, of excluding equivalents of the features shown anddescribed or portions thereof, it being recognized that the scope of theinvention is defined and limited only by the claims which follow.

1. A method of determining isometric relationships in an articulatedmammalian joint, comprising: (a) identifying a reference point on animage of one bone in said joint and an isometric point on an image of asecond bone in said joint which appears isometric to said referencepoint in at least two images of the joint, said two images respectivelyshowing said joint in flexed and extended positions; (b) providing ameasuring and positioning device having a body and two locating portionsassociated with said body, at least one of which is capable of movementrelative to the other; (c) identifying said reference point on said onebone in said mammalian joint; (d) holding a first one of said locatingportions at said reference point on said mammalian joint; and (e)concurrently identifying said isometric point on said second bone insaid mammalian joint by holding a second one of said locating portionsadjacent to said second bone in said mammalian joint while moving saidmammalian joint to each of said flexed and extended positions.
 2. Themethod of claim 1 including the step of positioning said two locatingportions at a distance from each other corresponding to a distancemeasured between said reference point and said isometric point in saidimages.
 3. The method of claim 1 wherein each said locating portion hasa marking element associated therewith.
 4. The method of claim 3 furthercomprising the step of marking said reference point on said first bonewith one said marking element.
 5. The method of claim 4 furthercomprising the step of marking the isometric point on said second bonewith the other said marking element.
 6. The method of claim 3 whereinsaid marking elements are substantially perpendicular to said body. 7.The method of claim 1 wherein said mammalian joint is a non-humanmammalian joint.
 8. The method of claim 1 wherein said mammalian jointis a canine stifle joint.
 9. The method of claim 1 wherein said imagesare radiographic images.
 10. The method of claim 1 wherein saidmeasuring and positioning device comprises two arms connected by atleast one pivot joint.
 11. The method of claim 1 wherein each saidlocating portion includes a receptacle capable of holding one of saidmarking elements.
 12. The method of claim 11 wherein said markingelements are wires.
 13. A device for locating a pair of isometric pointsin a mammalian joint, comprising: (a) two arms interconnected with eachother, and each said arm having a distal end; (b) each of said distalends having a locating portion associated therewith, and said arms beingmovable with respect to each other so as to adjust a separation distancebetween said locating portions; and (c) a fastener associated with atleast one of said arms and arranged to hold said locating portions at aselected said separation distance from each other.
 14. The device ofclaim 13 wherein each said locating portion has a marking elementassociated therewith.
 15. The device of claim 14 wherein said markingelement is capable of being temporarily affixed to an isometric point.16. The device of claim 14 wherein said marking elements aresubstantially perpendicular to said arms.
 17. The device of claim 13wherein said mammalian joint is a non-human mammalian joint.
 18. Thedevice of claim 13 wherein said mammalian joint is a canine stiflejoint.
 19. The device of claim 13 wherein said locating portions includerespective receptacles each capable of holding a respective markingelement.
 20. The device of claim 14 wherein said marking elements arewires.
 21. The device of claim 13 further comprising a scale associatedwith said arms and providing an indication of said separation distancebetween said locating portions.
 22. A device for locating a pair ofisometric points in a mammalian joint, comprising: (a) a body; (b) apair of locating portions associated with a said body, at least one ofsaid locating portions being adjustably located with respect to saidbody; and (c) a scale capable of providing an indication of a separationdistance between said locating portions.
 23. The device of claim 22wherein each said locating portion has a marking element associatedtherewith.
 24. The device of claim 23 wherein each said marking elementis capable of being temporarily affixed to an isometric point.
 25. Thedevice of claim 23 wherein each said marking element is substantiallyperpendicular to said arms.
 26. The device of claim 13 wherein saidlocating portions include respective receptacles each capable of holdinga respective marking element.
 27. A method of locating a pair ofisometric points within a mammalian joint, comprising: (a) obtainingimages of said mammalian joint respectively in its flexed and extendedpositions; (b) on the images, identifying a first point on a first bonein said joint; (c) on the images, identifying a second point on a secondbone in said joint, said second point being separated from said firstpoint by a distance that is equal when said joint is in full flexion andin full extension; and (d) thereafter locating within said mammalianjoint said first and second points previously identified on said images.28. The method of claim 27 wherein said joint is a canine stifle joint.29. The method of claim 28 wherein said first bone is a tibia and saidsecond bone is a femur.
 30. The method of claim 27 including the furtherstep of surgically exposing said joint prior to locating said first andsecond points in said joint.
 31. The method of claim 27 wherein saidimages are radiographic images.
 32. The method of claim 27 including thefurther step of measuring a first distance between said first and secondpoints within said joint when said joint is fully flexed; measuring asecond distance between said first and second points when said joint isfully extended; thereafter if said first and second distances areunequal adjusting said second point on said femur; thereafter againmeasuring said first and second distances; and repeating said steps ofadjusting and measuring until said second point is located where saidfirst and second distances are equal.
 33. The method of claim 27 whereinsaid joint is a canine stifle joint.
 34. A method of providing astabilizing extracapsular surgical repair for an articulating jointbetween two bones in a mammalian subject, comprising: (a) obtaining apair of images, a first image of said pair showing said articulatingjoint in a fully flexed position and a second image of said pair showingsaid articulating joint in a fully extended position; (b) in said imagesidentifying a pair of points between which to provide an extracapsulartension-carrying structure interconnecting said two bones, said pair ofpoints being a reference point on a first one of said two bones and anisometric point on the second one of said two bones, said reference andisometric points being located in said joint so as to be separated by aseparation distance that is equal in both of said first and secondimages; (c) providing a measuring and locating device having: (i) abody; (ii) a pair of locating portions associated with a said body, atleast one of said locating portions being adjustably located withrespect to said body; and (iii) a scale capable of providing anindication of a separation distance between said locating portions. (d)locating said reference point in said first one of said bones in saidarticulating joint in said subject; (e) thereafter, locating a trialisometric point on said second one of said bones in said articulatingjoint in said subject by fastening a first marking element at saidreference point and holding a second marking element in said secondlocating portion of said device at said separation distance with saidarticulating joint in a first one of a fully extended position and afully flexed position; (f) moving said articulating joint to the otherone of said fully extended and fully flexed positions and observingwhether said reference point and said trial isometric point are thenseparated by said separation distance; and adjusting the position ofsaid second locating member with respect to said trial isometric pointuntil an isometric point is located on said second one of said bones ofsaid articulating joint; and (g) surgically attaching a tension-bearingrepair structure to said bones as necessary to provide tension-bearingstructure extending between respectively said reference point and saidisometric point as thus located in said joint.
 35. The method of claim34 wherein one of said locating portions includes a threaded componentadjustably carried in said locating portion.
 36. The method of claim 34,when said device includes a releasable fastener selectively holding saidlocating portions at a predetermined distance from each other.
 37. Themethod of claim 34, including the further step of using said scale andthereby verifying that said separation distance between said referencepoint and said isometric point is equal when said joint is flexed andwhen it is extended.
 38. The device of claim 13 wherein said receptaclesare oriented parallel with each other.
 39. The device of claim 13including a releasable fastener arranged to hold said locating portionsselectively at a predetermined distance from each other.
 40. The deviceof claim 13 including a pair of marking elements capable of forming anopening in a bone and being inserted into said opening.
 41. The deviceof claim 13 wherein at least one of said locating portions is carried ona distal end of a first arm connected with said body through a pivotjoint.
 42. The device of claim 39 wherein said body has a second armattached thereto.
 43. The device of claim 39 wherein said pivot jointdefines a pivot axis and said locating portions include respectivereceptacles that are oriented to hold said marking members parallel withsaid pivot axis.